The present embodiments relate to receivers for sigma-delta beamforming for medical diagnostic ultrasound. In particular, the receiver includes a sigma-delta analog-to-digital converter for digital receive beamforming with different modes and/or different transducers.
Current ultrasound machines typically have a digital beamformer for B-mode, and possibly Pulsed-Wave (PW), and color flow Doppler modes. Nyquist sampling, multi-bit analog-to-digital converters (ADC) are typically used in this case. Since the data is typically not sampled at high enough frequencies for beamforming, data is estimated between samples using interpolation filters. Usually interpolation filters in digital beamformers have a high gate count because of the large coefficients and multipliers within the filter. Dynamic power dissipation is thus high because of the gate count. For continuous wave (CW) mode operation, a separate analog beamformer is provided for high dynamic range operation. Providing multiple beamformers for different modes increases system complexity and thus cost and physical space requirements increase.
Expanding applications to enhance workflow into portable hand-held ultrasound imaging devices require receiver architectures with significantly reduced power and costs while maintaining performance. Beamformers may be reduced in size or scaled. Small process geometries reduce the parasitic capacitances, which in turn reduces the power. However, scaling may only help incrementally through Nyquist converters such as flash or pipeline structures, because the ADCs may be susceptible to dynamic range limitations caused by process scaling. Thus, limited changes in power may be provided by scaling. As the profit margins in conventional ultrasound machines decrease, new receiver architectures are needed to reduce costs to maintain and/or increase profitability.
The connection from the transducer to the ultrasound system is also expensive. The cost of probe cable is often a significant proportion of the entire probe. Reducing the cable cost contributes to a big reduction in overall ownership costs, particularly for portable systems. Conventional analog cables (co-ax cables) are bulky as well. The bulkiness of the cable makes the probe hard to maneuver and contributes to repetitive muscle fatigue and injury.
A further complication is the use of different transducers with the same imaging system. Different transducers have different sized elements, such as a one-dimensional array having larger elements than a two-dimensional array. The differences in electrical impedance due to the different element sizes may limit the dynamic range of the receiver.